Fluid system resistance temperature compensation

ABSTRACT

Temperature compensation for fluid systems having fluid restrictors therein. Each restrictor is established as a laminar flow element. The result is an essentially constant flow ratio as between restrictors with temperature change. As an example, a digital to analog converter system is shown.

United States Patent Paul M. 11161106611 lnventor I50] FieldoiSearchl38/42.44. Newton Center. Mass. 137/85. 82. 608 235/201 AppLNo 834,846Filed June 19, 1969 I56] References Cited Patented .Iune 22.1971 UNITEDSTATES PATENTS Assign" mmhmcmmy 1.964.300 6/1934 Perry 1 .7 138/42 uxFMMMW- 3,220,256 11/1965 We1chbrod... 1ss/44x 3,266,380 8/1966Eige........ l37/85X 3.455.319 7/1969 Hogel...-. 137/85 PrimaryExaminer-Alan Cohan 1 1.0111 SYSTEM RESISTANCE TEMPERATURE AmmbumnCOMPENSATION icwmnnwmg Figs ABSTRACT: Temperature compensation for fluidsystems U.S. CL. .1 137/82, having fluid restrictors therein. Eachrestrictor is established 137/86, 137/608, l38/42, 235/201 as a laminarflow element. The result is an essentially constant lnt.C|.. v F151:3/14, flow ratio as between restrictors with temperature change. As

006d 3/00 an example, a digital to analog converter system is shown.

PATENTED JUH22 l9?! SHEET 2 BF 2 A 6m mTm v mm vm Smh\ N N 0- ON C m wINVENTOR. PAUL M. BLAIKLOCK AGENT- FLUID SYSTEM RESISTANCE TEMPERATURECOMPENSATION This invention relates to fluid operated instrumentationwherein fluid flows and pressures are used in situations such asmeasurement or control of processes or energy or parameters of these, inwhich fluid restrictors, resistances, are used as part of systems insuch instrumentation.

This invention relates more specifically to problems created in suchinstrumentation by temperature changes and provides means of achievingtemperature compensation.

ln pneumatic systems, restrictors are subject to flow change withtemperature change, with consequent potential of error in the systems.This flow change results from viscosity change since viscosity is astrong function of temperature.

This invention effects temperature compensation on the basis that inlaminar flow, change in resistance is mainly due to change in viscosity.Mainly due in the order of 90 percent. In gases, increased temperatureresults in increased viscosity and consequently decreased flow.

Flow is laminar, viscous or streamline when the Reynolds number is lessthan 2100.

Thus, in order to make flow through a pneumatic restrictor responsive totemperature change is a usefully repeatable manner, the restrictor is tobe formed and dimensioned, in view of the nature of the gas to be usedand the flows and pressures of its use, to achieve laminar flow in therestrictor.

Accordingly, this invention provides that in a system including two ormore operationally sensitive restrictors, flow through these restrictorsis made to be laminar. Thus, temperature compensation is accomplished inthat the ratio of flow as between such restrictors remains essentiallyconstant with temperature change.

As a vehicle of illustration, this invention is set forth herein asapplied to a digital to analog converter system of pneumatics, in whicha control loop maintains a constant pressure in a manifold, from whichpneumatic bleeds are established in response to a digital input patternas applied to a matrix of pneumatic restrictor systems. The control inmaintaining the manifold pressure, produces an analog output signalrepresentative of the digital input signal.

In this converter system, a summing, reference restrictor is used in thecontrol loop, and this restrictor, with the bleed restrictors, are allsensitive in the operation of the system. That is, errors related to therestrictors, especially as to temperature change errors, go to thecharacter of the output of the system. a

In this example of this invention, all these restrictors are made toachieve laminar flow, and in consequence, the flow ratio pattern betweenall these restrictors is maintained essentially constant withtemperature change, and temperature compensation is achieved.

Other objects and advantages of this invention will be in part apparentand in part pointed out hereinafter and in the accompanying drawings,wherein:

FIG. I is a schematic illustration of a group of fluid resistances inaccordance with this invention;

FIG. 2 is a structural showing of a single resistance, in one formthereof, as a sandwich structure, in plan, with partial cutaway, andaccording to this invention;

FIG. 3 is a section of the structure of FIG. 2, as if it were whole,taken on line 3-3; and

FIG. 4 is a digital to analog fluid converter system as an example of atemperature compensation system according to this invention.

In the FIG. I schematic, a digital matrix of restrictors, each andtogether according to this invention, are shown as spiral form passagesR, through R, in ascending logic flow capacities in the relative orderof I, 2, 4, 8, l6 and so on.

Each of the restrictors R ,-R,, are laminar flow passages, soconstructed by length and form, in view of the air pressures of theparticular application with which they are to be involved -FIG. 4illustrates one such application.

In FIG. I, a common supply manifold 18 is provided for all therestrictors and each restrictor has its own outlet, at the intemalterminus of its spiral, as exemplified in R at 1. These restrictors areformed, as in FIGS. 2 and 3, in a sandwich structure with a base 2, inwhich the restrictor passages as R,,, may be formed by etching or othersuitable slot forming means, in the surface of the base 2. Thereafter acover plate 3 is placed over this surface to close off the open side ofthe slot and form a continuous spiral pneumatic restrictor passage.

This structure is suitable for one or more restrictors, and lends itselfto the modern needs of simplification and miniaturization.

FIG. 4 illustrates a digital to pneumatic analog converter, which is acombination of a digital input matrix of fluidic resistances and apneumatic analog controller, with a manifold supply to the resistancesmaintained at constant pressure by the controller, and a pneumaticanalog output to a value established by the controller change necessaryto maintain the manifold pressure.

This invention relates to digital to analog converters, in the FIG. 4system, the digital input may be pneumatic, electrical or mechanical,and the analog output is pneumatic. This is a pneumatic system to whichdigital input signals may be applied to switches controlling R R,....Rincluding a pneumatic controller which maintains a fixed pressure at thedigital input, and has an analog pneumatic output whose pressure levelis representative of the digital input signal, this pressure level beingaccomplished through operation of the pneumatic controller in the courseof its changes as necessary to maintain the fixed pressure at thedigital input.

The controller of this invention is of the nature of the disclosure inpatent application to Prescott et al., Ser. No. 772,787, filed Nov. 1,1968 and entitled Pressure Device Having Layered Construction andPivoting Seal with Operator. The abstract of the disclosure of thispatent application is as follows:

In a multilayer sandwiched-type of construction, an operator activatedby at least one pressure chamber is brought through a sealingconfiguration which also provides for pivoting of the operator; theoperator itself is formed from a layer of the sandwiched constructionand the sealing at the operator pivot is formed from sealing layers ofthe sandwiched construction; the operator layer may be backed by aresilient sheet layer for sealing the pressure chamber actuating theoperator; this construction may be readily adapted to a plurality ofpressure chambers employed in conjunction with motion-sensing devices,or alternatively weight and springs, to perform the functions of alarms,relays, repeaters, amplifiers, and a variety of other pneumatic devices.

The illustration of FIG. 4 is of an 8 bit digital to analog pneumaticconverter which accepts parallel binary inputs, and transmits a 3-15p.s.i. analog signal.

One application of this converter is in a fluidic programmer, and it iscapable of accepting low level fluidic signals for such purpose. It maybe used in conjunction with a punched card and pneumatic reader, tocontrol rates, set points, or values in an analog fashion.

The system of FIG. 4 comprises a pneumatic reset controller 10, with acontrol loop associated therewith including an output passage 11 througha flow booster 12, past an analog output passage from the control loopat 13, through a summation resistor 14 through a supply manifold 15, andfinally back to the controller 10 as a measurement input 16, inopposition to a set point input 17 to the controller.

A digital input is generally indicated at 18, and comprises a resistancematrix to the supply manifold 15 such that the individual flows throughthe individual digital resistances, for a given differential pressure,are in binary ascending ratio, as I, 2, 4, 8, etc.

The function of the controller 10 is to maintain the pressure in thesupply manifold I5 essentially constant. The resistance matrix I8 is therecipient of digital input signals, whereas the result of theapplication of a digital input combination to the matrix 18 is a likecombination of air bleeds to atmosphere through the specific resistanceswhich are individual to the various units of the particular digitalinput combination.

The result of each bleeding of air to atmosphere is a tendency tolowering of the pressure in the supply manifold 15. The controllerresponds, to counteract this tendency, and the amount of this response,as necessary to achieve again a balanced condition in the control loop,is a measure of an analog output through 13, representative of theparticular digital combination input signal.

The flow booster 12 provides the volume requirements of the supplymanifold 15 and isolates the controller 10 from the loads producedthrough the digital input resistance matrix l8.

As an example of a controller 10, suitable for the system of thisinvention, the drawing controller illustration is a representation ofone form of the previously mentioned disclosure in the patentapplication to Prescott et al. In this illustrative application, aproportional-reset controller form is used with pressure chambers 19,20, 21 and 22 as measurement, setpoint, reset, and supply-bleed chambersrespectively. A reset resistance-capacity system 23 and 24 is connectedbetween the chambers 21 and 22.

Throughout the drawings, an illustration of one working example, variouslabels as to flow and pressure are shown. These are set forth simply asguide line values.

In the FIG. 4 resistance matrix 18, there are 8 digital bits, each onecomprising an air passage from the manifold 15 to atmosphere at 25through a resistance such as 26, with switch 27 in the passage betweenthe resistance 26 and atmosphere at 25.

Thus, in a digital input of O or 1 to the switch 27 the switch 27 may beoperated to open or close the passage from the manifold 15 toatmosphere, to close off that particular bit, or

to bleed it 011' to atmosphere as the case may be.

In the showing of FIG. 4, the R, bit digital input is shown as logiczero and the fluid line is open to flow from the manifold 15 toatmosphere at 25. In the illustrative input showing, the R, but has alogic one' input and the fluid line is broken from the manifold toatmosphere. The switch condition of R in FIG. 4 involves a shutoff offlow from the manifold to atmosphere so that. there is essentially zeroair flow from the manifold 15 through R,

In the FIG. 4 system, the digital restrictors R, through R,,, and thesumming, reference restrictor 14, all go to the essence of the operationof the system, in the sense that they are subject to error underconditions of temperature change.

In this invention, however, all of these restrictors are established aslaminar flow elements. Accordingly, the flow ratio between theserestrictors is maintained essentially constant with temperature change.

The other restrictors of the FIG. 4 system are not sensitive in thetemperature error sense and flow therethrough need not be laminar. Thep.s.i. supply restrictor to the controller l0 is one of these, as is thefeedback restrictor 23 to the con troller.

While it is not usually desirable, from a space standpoint, to havestraight laminar restrictors, these are within the scope of thisinvention.

The R,R, and 14 restrictors are shown in FIG. 4 schematically. Theirpreferred form is that of FIGS. 1, 2 and 3.

This invention therefore provides new and useful means for temperaturecompensation in fluid systems, as related to fluid restrictors therein,in the form of laminar flow through such restrictors, to maintainessentially constant ratio of flow through these restrictors undertemperature change conditions.

As many embodiments may be made of the above invention, and as changesmay be made in the embodiment set forth above without departing from thescope of the invention, it is to be understood that all matterhereinbefore set forth and in the accompanying drawings is to beinterpreted as illustrative between said restrictors remains essentiallyconstant with temperature change applied alike to said res rictors, saidsystem comprising a fluid control loop with one of said restrictors insaid loop, and a group of restrictors as means for selectively providingdifferent bleeds to atmosphere from said loop,

said group of restrictors being provided in a structure comprising aplate, a group of channel forms in one face of said plate, and a coverplate overlying said channel plate whereby said channel fonns becomeperipherally closed passageways;

said passageways comprising a manifold passage as a part of said controlloop with a control loop input to said manifold at one end of saidmanifold and an exit to said control loop at the other end of saidmanifold, and a graduated series of single flat plane spiral restrictorpassages as graduated leaks to atmosphere;

each of said spiral restrictor passages having one end individuallyconnected to said manifold and the other end exited to atmosphere fromthe central point of its spiral, with said spirals of sufficient lengthand suitable form to establish laminar flow therethrough according tooperating flow parameters; and

said manifold ends of said passages together forming a central,trunklike stem grouping of parallel passages, with said individualpassages flowering laterally from said stem grouping into individualspirals in essentially symmetrical increments of separated placement insaid structure.

1. Temperature compensation means as between fluid restrictors in afluidic system, comprising said restrictors as laminar flow elements insaid system such that flow ratio as between said restrictors remainsessentially constant with temperature change applied alike to saidrestrictors, said system comprising a fluid control loop with one ofsaid restrictors in said loop, and a group of restrictors as means forselectively providing different bleeds to atmosphere from said loop,said group of restrictors being provided in a structure comprising aplate, a group of channel forms in one face of said plate, and a coverplate overlying said channel plate whereby said channel forms becomeperipherally closed passageways; said passageways comprising a manifoldpassage as a part of said control loop with a control loop input to saidmanifold at one end of said manifold and an exit to said control loop atthe other end of said manifold, and a graduated series of single flatplane spiral restrictor passages as graduated leaks to atmosphere; eachof said spiral restrictor passages having one end individually connectedto said manifold and the other end exited to atmosphere from the centralpoint of its spiral, with said spirals of sufficient length and suitableform to establish laminar flow therethrough according to operating flowparameters; and said manifold ends of said passages together forming acentral, trunklike stem grouping of parallel passages, with saidindividual passages flowering laterally from said stem grouping intoindividual spirals in essentially symmetrical increments of separatedplacement in said structure.